Tacky hot melt compositions have been used widely in the adhesive industry for a wide range of applications such as for pressure sensitive adhesives due to their ability to adhere to a wide variety of substrates. A primary property of a hot melt pressure sensitive composition is that it remain tacky at room temperature so that it may be adhered to substrates when it has completely cooled from its molten state. Examples of applications which require this property are tape and label applications. Paper, polyethylene, polypropylene or other such substrates may be coated with the tacky hot melt composition, covered with release liner, and then shipped this way for later applications such as for labels used on various containers, books, magazines, or envelopes just to name a few.
The use of tacky hot melt compositions in other applications has been precluded by the fact that they remain tacky. Yet it may be desirable to use these soft and very flexible compositions for other applications. One such application is the formation of articles by injection molding. Some articles formed by injection molding include shoe soles, drum pads, therapeutic hand exercising grips, shock absorbers, acoustical insulators, chair pads and imitation skin for use in the entertainment industry but this list is not exhaustive.
The tackiness exhibited by these hot melt pressure sensitive adhesives also makes them difficult to handle. They may adhere to skin, clothing, application equipment, floors, or other places that are undesirable. Many packaging methods have been devised to avoid the problems encountered in the handling of these hot melt pressure sensitive compositions.
Hot melt adhesives are supplied as pellets, pillows as disclosed by German Pat. 22 48 046, slats or chicklets, blocks, and cakes.
A further problem encountered with hot melt pressure sensitive adhesives is that the tackiness may result in blocking individual pieces together resulting in a large mass in the shipping containers. This makes it difficult to get the adhesive into many different types of hot melt premelter tanks used in the industry.
U.S. Pat. No. 3,723,035 discloses a machine performing an improved method of packaging a hot melt adhesive. This produces an end product known as pillows to one of skill in the art. These pillows can be coextruded with a non-tacky polymer such as polyethylene for producing pressure sensitive adhesives that are tacky at room temperature. This coextrusion coating prevents the pillows from blocking together in a solid mass at room temperature. Using this method, once the coextruded pillows are melted for use on an application line, the hot melt composition again becomes tacky when it returns to room temperature.
French Pat. No. 2,544,654 published Oct. 26, 1984 discloses forming a tackless hot melt by adding the molten hot melt to a mold which contains a preformed support layer having a transfer film which is compatible with the hot melt.
U.S. Pat. Nos. 4,748,796 issued Jun. 7, 1988 and 4,755,245 issued Jul. 5, 1988 disclose forming a protective coating for an adhesive material by electrostatically coating a mold or cavity with a powder screen and then pouring hot melt into the mold.
French Pat. No. 2,601,616 published Oct. 22, 1988 discloses forming blocks of hot melt pressure sensitive adhesive by casting the adhesive into molds precoated by spraying with a film of non self-sticking hot melt material.
German Pat. Nos. DE 31 38 222, DE 32 34 065, and DE 36 25 358 teach coating or wrapping a formed hot melt block with various types of film.
U.S. Pat. No. 5,257,491 to Rouyer et al. teaches a method of packaging a hot melt adhesive composition wherein the adhesive composition is sufficiently solidified or when flowable.
U.S. Pat. No. 5,401,455 to Hatfield et al. issued Mar. 28, 1995 teaches a method for packaging hot melt adhesive compositions comprising the use of a mold being in contact with a refrigerant gas or liquid heat sink. Hatfield teaches that when a hot melt adhesive is poured into a cavity lined with film in its molten state, the adhesive is fused to some extent with the film. According to Hatfield, this in turn allows some mixing and compatibilizing of the film, improving the opportunity for more complete mixing.
U.S. Pat. No. 5,057,571 to Malcolm et al. discloses at column 8 line 59 to column 9 line 14 a method for pelletizing a preblend of a radial block copolymer and a tackifying resin. This preblend is then used to make hot melt adhesives for disposable article construction. The preblend is manufactured on an extruder. The pelletized preblend was then used to make an adhesive using conventional hot melt mixers. This is a two step process of making hot melt pressure sensitive adhesives, and it was never intended to teach making a finished product in a free-flowing pellet form.
The current inventors have found a polymeric composition in a free-flowing pellet form that can be either a hot melt pressure sensitive adhesive or a polymeric composition that has a surface that remains tack-free after melting and resolidification.